In mobile communication networks, such as LTE (Long Term evolution), random access channels are used by mobile communication terminals to initiate communication with a base station using a cell of the base station. The mobile communication terminal initiates this by sending a preamble, consisting of a number of symbols, on the random access channel (which is common to all such initiation for the cell) with a preamble id (RAPID, Random Access Preamble ID), for LTE between 0 and 63, selected from a group of preambles which are valid for the cell of the base station. In LTE, for the same cell, the valid preambles make use of a finite set of symbol sequences (root sequences). Different preambles are obtained from the same symbol sequence by cyclically shifting the symbols of the sequence.
If two neighbouring cells use the same root sequences for random access, this will cause unnecessary random access load. For each random access procedure in one cell there is a risk that a false preamble is detected in the other. As the number of preambles that can be handled simultaneously in one cell is limited, this will affect random access performance, e.g. by increasing the average delay before the mobile communication terminal establishes communication with the cell, and can also increase the risk of signalling congestion.
In WO 2010/071561 root sequence conflicts are detected and trigger reconfiguration of the used root sequences of the processing base station, neighbouring base stations and optionally of the base stations neighbouring the neighbouring base stations. However, the presented solution requires new communication between base stations and it is not trivial to resolve conflicts in root sequence usage between multilevel neighbours.